Calibration of temperature sensing circuitry in an electronic device

ABSTRACT

Temperature sensing circuitry is used for thermal management of an electronic device. The temperature sensing circuitry includes at least one thermistor placed at or near a component of the electronic device. The temperature sensing circuitry also includes a high-precision resistor for calibration purposes. The resistance of the resistor is equivalent to the resistance of the thermistor at a reference temperature. A calibration reading is obtained using a set current that is being passed through the resistor. An error present in the temperature sensing circuitry is determined based on the calibration reading and a design value. A temperature measurement associated with the component is then made using the thermistor, while the set current is being passed through the thermistor. The error is corrected in the temperature measurement of the component. Other embodiments are also described.

This application is a divisional of co-pending U.S. patent applicationSer. No. 12/130,650, filed on May 30, 2008.

TECHNICAL FIELD

An embodiment of the invention relates generally to thermal management,and more particularly, to a temperature sensing system in a portableelectronic device. Other embodiments are also described.

BACKGROUND

Portable electronic devices are becoming increasingly popular. Examplesof portable electronic devices include laptop computers, personaldigital assistants (PDAs), mobile telephones, media players, and hybriddevices that provide a combination of the functionalities of the abovedevices.

To satisfy consumer demand for small and lightweight portable electronicdevices, manufacturers are continually striving to reduce the size ofthe devices while providing enhanced functionality. When electroniccomponents are tightly packaged in a small device, heat dissipationbecomes an important issue. As most consumer electronics cannot functionproperly at a high temperature for an extended period of time,manufacturers often place temperature sensors, such as thermistors, tomonitor the internal temperature of the electronic devices. Thesetemperature sensors allow out of range temperature scenarios to berecognized, so that mitigation actions can be taken before systemfailure.

Conventionally, temperature sensors in a device are calibrated to ensuretheir accuracy, by heating up the device to a known temperature. Theoutput of the temperature sensors is then compared with an expectedtemperature to determine an error in the sensor output. This error isthen stored in the device for later use. Thereafter, the device, whilebeing used “in the field”, then automatically compensates the readingsfrom its sensors using the stored error values. However, theconventional calibration process requires heating up the motherboard ofa device in an oven, which is a complex process in terms of time andresources. Further, the conventional calibration process cannot beperformed in the field, i.e. after the devices have been packaged andshipped by its manufacturer for resale.

SUMMARY

Temperature sensing circuitry is used for thermal management of anelectronic device. As modern electronic devices often operate near hotlimits to maximize performance, the temperature measurements taken usingthe sensing circuitry in every manufactured device should be accurate,to ensure that the hot limit is never exceeded and that the performanceof the device is not unduly lowered. Reliable and low cost calibrationof the temperature sensing circuitry is thus needed.

In one aspect of the invention, the temperature sensing circuitryincludes at least one thermistor placed at or near a component of theelectronic device. The temperature sensing circuitry also includes ahigh-precision resistor for calibration purposes. The resistance of theresistor is equivalent to the resistance of the thermistor at areference temperature. A calibration reading is obtained using a setcurrent that is being passed through the resistor. An error present inthe temperature sensing circuitry is determined, based on thecalibration reading and its design value. A temperature measurementassociated with the component is then made using the thermistor, whilethe set current is being passed through the thermistor. The determinederror is applied to correct the temperature measurement of thecomponent. Other embodiments of the invention are also described below.

Embodiments of the present invention include apparatuses and dataprocessing systems which perform these methods, and computer readablemedia which when executed by data processing systems cause the systemsto perform these methods.

Other features of the present invention will be apparent from theaccompanying drawings and from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention are illustrated by way of example andnot by way of limitation in the figures of the accompanying drawings inwhich like references indicate similar elements. It should be noted thatreferences to “an” or “one” embodiment of the invention in thisdisclosure are not necessarily to the same embodiment, and they mean atleast one.

FIG. 1 is a diagram of illustrative temperature sensing circuitry inaccordance with an embodiment of the present invention.

FIG. 2 is a diagram of an illustrative temperature coefficient curve ofa thermistor used in the temperature sensing circuitry in accordancewith an embodiment of the present invention.

FIG. 3 is flow diagram of an illustrative process for calibrating thetemperature sensing circuitry in accordance with an embodiment of thepresent invention.

FIG. 4 is a circuit diagram of an illustrative wireless electronicdevice in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The following description and drawings are illustrative of the inventionand are not to be construed as limiting the invention. Numerous specificdetails are described to provide a thorough understanding of the presentinvention. However, in certain instances, well known or conventionaldetails are not described in order to avoid obscuring the description ofthe present invention. References to one or an embodiment in the presentdisclosure are not necessarily references to the same embodiment; and,such references mean at least one.

An electronic computing device typically generates heat in operation.After a period of operation, the temperature of the device may rise to alevel that causes damage to its internal electronics—a so-called hotlimit. To prevent heat damage, power settings of one or more of thedevice components can be dynamically adjusted based on the temperatureof the components. The adjustment in power settings reduces powerconsumption, which, in turn, reduces the temperature of the device.

In one embodiment, the electronic computing device includes atemperature sensing subsystem to monitor the temperatures of itscomponents. These components may be a heating generating component, acomponent sensitive to high temperature, a component near a heat source,a component distant from the main heat generating components, or othercomponents that are good indicators of internal, external, or ambienttemperatures of the device.

In one embodiment of the present invention, it is recognized that atemperature sensing subsystem can be calibrated with a high-precisionresistor. The resistor is chosen to have the equivalent resistance of athermistor at a reference temperature that is below the uppertemperature limit of the system. In one embodiment, the referencetemperature can be chosen to be in the proximity of the desiredoperating temperature of the system, which is near the hot limit.

FIG. 1 is a simplified block diagram of an embodiment of temperaturesensing circuitry 180 deployed within an electronic computing device100. Temperature sensing circuitry 180 includes one or more thermistors112-114 and a resistor 110, all of which are coupled to a thermalmonitor 135 via a plurality of I/O pins 165. In one embodiment, thermalmonitor 135 may be part of a single-chip circuit module 160, such as acellular baseband processor integrated circuit package, in a wirelesscommunication device. Resistor 100 is external to the integrated circuitpackage, and may be coupled to an unused thermistor input pin of theintegrated circuit package. For simplicity of illustration, resistor 110is shown as located next to thermistors 112-114. However, resistor 110may be located anywhere in device 100, and may not be located next to ornear thermistors 112-114.

Thermal monitor 135 includes a multiplexer 120, the output of which iscoupled to a current source 130 and an analog to digital converter (ADC)140. Current source 130 supplies a set current to drive a resistive loadin the temperature sensing circuitry 180, thereby providing a voltage atthe output of multiplexer 120 (i.e., at a point 170). ADC 140 convertsthe voltage at point 170 into a digital measurement. Electroniccomputing device 100 uses the digital measurements to monitor thetemperatures of its components, such that power consumption may bedynamically adjusted, thereby preventing damage to the electronicscaused by excessive heat.

In one embodiment, each of the thermistors 112-114 is placed near or ata component of electronic computing device 100 to measure thetemperature of the component. In an embodiment where electroniccomputing device 100 is a handheld wireless communication device, thecomponents for which the temperatures are measured may include abattery, a RF transmitter power amplifier, a subscriber identity module(SIM) card circuit, and other electronic modules. The SIM card circuitin a handheld device is generally located away from the main heatgenerating components; therefore, the temperature reading at the SIMcard circuit provides a thermal reading that is distant from the mainheat generating components and can be used to monitor the ambienttemperature of the device. Temperatures may also be monitored at or nearnon-electrical parts of the system for user satisfaction (e.g., toprevent a handheld device from overheating to cause user discomfort).The non-electrical parts may include the portion of the housing at theearpiece (receiver), and the center of the housing's back panel.

FIG. 2 illustrates the temperature-resistance curve 200 of an examplethermistor 112-114. Temperature-resistance curve 200 is also referred toas a negative temperature coefficient (NTC) curve, as the resistancedrops when the temperature increases. In one embodiment, a criticalthermal bound 210 of electronic computing device 100 is the upper boundof temperatures for which the operation of device 100 is optimized.Critical thermal bound 210 is near but below a hot limit of the device.For example, critical thermal bound 210 may be determined based on thesafety limit of the battery in device 100, a customer satisfactionlimit, and other factors. Device 100 may operate below critical thermalbound 210 with little or no performance impact caused by the thermalmanagement. When the temperature of device 100 rises to a point where itis likely to exceed critical thermal bound 210, thermal mitigationactions may be initiated to reduce the power consumption of device 100.Thus, the critical thermal bound 210 may be a relatively narrow range oftemperatures, e.g. at about 60 degrees+/−less than 2 degrees.

A reference temperature 220 is chosen near or in critical thermal bound210. Reference temperature 220 can be used to select the resistance ofresistor 110. In one embodiment, the resistance of resistor 110 ischosen such that it is equivalent to the resistance of thermistors112-114 at reference temperature 220. Thus, the point representing theresistance of resistor 110 and reference temperature 200 falls on thetemperature-resistance curve. Resistor 110 is a precision resistor thatfor example may be accurate to within approximately 0.1% or better. Thatis, the actual resistance of resistor 110 may be guaranteed by itsmanufacturer to be within approximately 0.1% of the design (ortheoretical) resistance value, or better. In comparison, thermistors112-114 may be substantially less accurate, e.g., accurate withinapproximately 1% of the design value. In one embodiment, the precisionresistor has an accuracy or tolerance at least an order of magnitude(factor of 10) better than that of the thermistors 112-114.

Referring again to FIG. 1, during operation of temperature sensingcircuitry 180, multiplexer 120 selects one of resistor 110 andthermistors 112-114 according to a selection signal 150. Selectionsignal 150 may be generated by a user command, a software-generatedcommand, or circuitry that resides within or outside of circuit module160. When one of the thermistors 112-114 is selected, multiplexer 120establishes a current path from the selected thermistor to ADC 140. Thecurrent supplied by current source 130 passes through multiplexer 120and the selected thermistor to establish a voltage at the input of ADC140, which is converted to a digital measurement by ADC 140. The digitalmeasurement can be converted to a temperature according to apredetermined conversion table or a conversion formula.

However, the digital measurement may deviate from the true temperaturevalue in device 100 due to the inaccuracy in thermistors 112-114,current source 130, ADC 140, as well as any other components in themeasurement path. For example, thermistors 112-114 may each have about1% of inaccuracy. Additionally, current source 130 and ADC 140 may eachhave about 2% of inaccuracy. The inaccuracy of these circuit elementsmay accumulate to produce a temperature measurement that is below orabove the true temperature value, by in this example 5%. In manyinstances, this may be too large a margin, because many specimens of thedevice 100 will, as a result, be operating less efficiently in thefield. To explain, consider the following example.

With +/−5% total inaccuracy, the thermal management system may have a“programmed hot limit” that is 5% less than the actual hot limit. Thishelps ensure that every manufactured device will be in compliance of theactual hot limit, despite some devices reading low and others high. Now,while the low devices may indicate the temperature to be as low as 55degrees, the high devices will indicate as high as 65 degrees, even whenthe actual temperature is 60 degrees. But due to the inaccuracy, thethermal management system running in the high devices may have to reduceperformance when the actual temperature is only about 50 degrees, almosta full ten degrees below the actual limit. As a result, consumers whohave by chance been given high devices may be experiencing noticeablylower performance levels than others who have low devices. Calibrationmay help reduce the total inaccuracy of the temperature sensingcapability.

To calibrate the circuit elements in temperature sensing circuitry 180,multiplier 120 selects resistor 110 to establish a path between resistor110 and ADC 140. The set current supplied by current source 130 flowsthrough resistor 110 to provide a voltage at the input of ADC 140. Inone embodiment, resistor 110 has a resistance that is the equivalent tothe resistance of thermistors 112-114 at the reference temperature,e.g., between about 55 to 60 degrees centigrade, depending on the typeof electronics used in the electronic computing device 100.

When resistor 110 is used, the digital measurement at the output of ADC140 includes an error present in resistor 110, current source 130 andADC 140. As current source 130 and ADC 140 are far less accurate thanresistor 110, the inaccuracy of resistor 110 may be negligible in theresulting digital measurement. For example, if resistor 110 has the sameresistance as a thermistor 112-114 at 60 degrees centigrade, the ADCoutput per manufacturer or design specification may be, illustratively,1000 (before conversion into a temperature). However, due to the errorsintroduced by current source 130 and ADC 140, the actual digitalmeasurement may be, illustratively, 980. The −20 units of difference canbe used to calibrate temperature sensing circuitry 180 in order toremove the errors introduced by current source 130 and ADC 140. Aprocess for calibrating temperature sensing circuitry 180 is describedin greater detail with reference to FIG. 3 below.

FIG. 3 is a flow diagram of an embodiment of a process 300 forcalibrating temperature sensing circuitry 180 of FIG. 1. Process 300 maybe implemented with software, firmware, and/or hardware in electroniccomputing device 100. In one embodiment, process 300 may be executed bycircuit module 160 of FIG. 1, a processor of electronic computing device100, or other processing circuits of electronic computing device 100.

Referring to FIG. 3, a calibration baseline is established by usingresistor 110 of FIG. 1. At block 310, in response to selection signal150, multiplexer 120 establishes a current path through the resistor110. At block 320, the output of ADC 140 is recorded in local storage asa calibration measurement. At block 330, the calibration measurement iscompared with a design value to compute an error. The design value isbased on the manufacture or design specification of ADC 140, currentsource 130, and resistor 110. At block 340, a thermistor measurement istaken (using the ADC 140) by selecting one of thermistors 112-114 andestablishing the same current through the selected thermistor. At block350, the error is applied to the thermistor measurement to calculate acorrected measurement. At block 360, the corrected measurement isconverted into a temperature value using a conversion table or aconversion formula. The temperature value indicates the temperature ofthe component associated with the selected thermistor. As analternative, the conversion of the thermistor measurement to thetemperature value can be performed before applying the computed error toobtain the corrected measurement. That is, the conversion operation ofblock 360 may be performed on the error at block 330 and on thethermistor measurement at block 340. The converted error can then beapplied to the converted thermistor measurement to obtain a correctedtemperature value.

The temperature value may be further processed by software run bycircuit module 160 or other software/hardware modules in electroniccomputing device 100. At block 370, the temperature value is compared toa predefined threshold temperature. Based on the comparison result, atblock 380, power consumption of electronic computing device 100 may beincreased or decreased to adjust the temperature in device 100. In oneembodiment, power consumption may be managed by a separate circuitmodule in device 100, such as a power management unit. An embodiment ofa power management unit will be described with reference to FIG. 4.

A feature of process 300 is that it can be performed at any time of thelifecycle of the electronic computing device 100, for as many times asnecessary. The calibration measurement using resistor 110 may be readevery time the temperatures of device components are measured. Process300 does not involve heating up device 100 in an oven, which is acomplex process in terms of time and resources.

In one embodiment, the electronic computing device 100 of FIG. 1 may bea portable electronic device, as that is where the benefits of theinvention will be most apparent. However, the invention could if desiredbe implemented in a desktop personal computer, for instance. Theportable electronic device may be a laptop computer, a handheldelectronic device (such as a personal digital assistant or a handheldgaming device), a media player, or a wearable electronic device.Examples of wearable electronic devices include wrist-watch devices,pendant devices, headphone and earpiece devices, and other wearable andminiature devices. In some embodiments, the portable electronic devicemay be provided with wireless communication capability, such as cellulartelephones, cordless telephones, remote controllers and globalpositioning system (GPS) devices. The wireless electronic devices may behybrid portable electronic devices that combine the functionality ofmultiple conventional devices. Examples of hybrid portable electronicdevices include a cellular telephone that includes media playerfunctionality, a gaming device that includes wireless communicationscapability, a cellular telephone that includes game and email functions,and a portable device that receives email, supports mobile telephonecalls, has music player functionality and supports web browsing. Theseare merely illustrative examples.

In one embodiment, the portable electronic device may include circuitryto run software applications, such as internet browsing applications,voice-over-internet-protocol (VoIP) telephone call applications, emailapplications, media playback applications, operating system functions,etc. The portable electronic device may also be used to implementcommunications protocols, such as Internet protocols, wireless localarea network protocols (e.g., IEEE 802.11 protocols, also known asWi-Fi®), protocols for other short-range wireless communications linkssuch as the Bluetooth® protocol, protocols for handling 3Gcommunications services, 2G cellular telephone communications protocols,etc. The term “2G communications” herein refers to traditional cellulartelephone and data communications. An example of 2G cellular telephonesystems are those based on Global System for Mobile Communication (GSM)systems. The term “3G communications” herein refers to communicationswith newer formats that support increased speeds and may be used forboth data and voice traffic. Such formats may use wide bandcode-division multiple access (CDMA) technology. In some embodiments,wireless signals can also be sent using light (e.g., using infraredcommunications).

In accordance with an embodiment of the present invention, anillustrative portable electronic device 400 with wireless communicationscapability is shown in FIG. 4. It is understood that for clarity of thedescription, components of portable electronic device 400 that are notgermane to this disclosure are not described.

As shown in FIG. 4, portable electronic device 400 includes a processor450, which serves as the main processor for implementing user functions.In this capacity, processor 450 may be used to run applications for theuser such as media playback applications, communications applications,calendar applications, games, notepad applications, businessapplications, etc.

The operations of processor 450 may be supported using a memory 460 thatcomprises one or more memory modules. Memory 460 may include arelatively small memory module (e.g., 8 Mbytes) that is used to storeboot instructions. Memory 460 may also include a larger memory module(e.g., 4-16 Gbytes) that is used to store applications and data, and astatic Random Access Memory (RAM) for fast memory operations. Memory 460may include nonvolatile and volatile memory modules.

Device 400 also includes a baseband processor 452 to provide dataprocessing function for the data received and the data to betransmitted. Baseband processor 452 may receive data from processor 450,audio data from an audio codec 414, GPS data from an antenna 462, orother sources.

Baseband processor 452 may, if desired, be implemented as a singleintegrated circuit. Baseband processor 452 may provide data to betransmitted to transceiver 454 (e.g., radio frequency (RF) transceivercircuitry that can handle 2 G operations and that can handle 3 Goperations using wide band code division multiple access techniques).Baseband processor 52 may be coupled to power amplifier circuitry 456(e.g., 2G GSM power amplifier circuit and 3G power amplifier circuitry).Memory 404 may be used to store data for baseband processor 452. Memory404 may be, for example, 8-16 MB of static random-access memory (SRAM).

Baseband processor 452 may include processing circuitry for handlingaudio signals. For example, baseband processor 452 may include a digitalsignal processor (DSP) block that performs functions such as noisesuppression, gain control, filtering, analog-to-digital conversion,digital-to-analog conversion, and vocoding (e.g., functions such ascompressing audio to phase-code-modulation-encoded signals fortransmission over a wireless network, voice decoding functions, etc.).

Audio codec 414 may reside on a separate chip to handle telephony audiosignals and other audio signals. For example, speakers and a microphonemay be coupled to audio codec 414.

Device 400 includes an antenna 462, which may further include apentaband cellular antenna and a dual band antenna. Illustratively, thepentaband antenna may be used to cover wireless bands at 850 MHz, 900MHz, 1800 MHz, 1900 MHz, and 2100 MHz, and the dual band antenna may beused to handle 1575 MHz signals for GPS operations, 2.4 GHz signals forBluetooth® operations, and 2.4 and 5.0 GHz for IEEE 802.11 operationsand wireless local area network (WLAN) operations.

Device 400 may be powered by a battery 483. During data transmission,power amplifier circuitry 456 may boost the output power of transmittedsignals to a sufficiently high level to ensure adequate signaltransmission. Battery 483 may be a lithium ion battery, a lithiumpolymer battery, or a battery of any other suitable type. Battery 483may be rechargeable and may be removed by an end user as necessary(e.g., when it is desired to replace a fresh battery).

Device 400 may include a subscriber identity module (SIM) connector 458and other ports 430. SIM connector 458 may be used to receive a SIM cardfor authorizing cellular telephone services. When the SIM card isinstalled in device 400, an authorized user may use device 400 for voiceand data wireless communications (e.g., using the 3G or 2G capabilitiesof devices 400).

Ports 430 may include power jacks to recharge battery 483 from a directcurrent (DC) power supply. Ports 430 may also include data ports toexchange data with external components such as a personal computer orperipheral, audio-visual jacks to drive a headphone, a microphone, aspeaker, a monitor, or other external audio-video equipment, a memorycard slot, etc. Digital video output signals from processor 450 may besupplied to video digital-to-analog converter (DAC) circuit 434. Theresulting analog video signals may be supplied to ports 430.

The functions of some or all of these components and the internalcircuitry of device 400 can be controlled using an interface device suchas a touch screen display.

A display 416 of the device 400 may be a liquid crystal diode (LCD)display, an organic light emitting diode (OLED) display, or any othersuitable display. The outermost surface of display 416 may be formedfrom one or more plastic or glass layers. If desired, touch screenfunctionality may be integrated into display 416 or may be providedusing a separate touch pad device.

Device 400 may have other user interface devices 472, such as buttons(e.g., alphanumeric keys, power on-off, power-on, power-off, and otherspecialized buttons, etc.), touch pads, key pads, keyboards, pointingsticks, click wheels, scrolling wheels, or other cursor control device,a microphone for supplying voice commands, a camera, or any othersuitable interface for controlling device 400. If desired, device 400can be controlled remotely (e.g., using an infrared remote control, aradio-frequency remote control such as a Bluetooth® remote control,etc.).

Device 400 may include other I/O devices 473, such as light-emittingdiodes (LEDs) to visually display the status of device 400, speakers togenerate sounds, a vibrator to generate vibration during silentoperations, etc.

In the embodiment shown in FIG. 4, thermal monitor 135 of temperaturesensing circuitry 180 (FIG. 1) resides in baseband processor 452. Forsimplicity of the circuit diagram, thermistors 112-114 and resistor 110are not shown in FIG. 4. Thermistors 112-114 may be placed near or atbattery 483, power amplifiers 456, SIM connector 458, or othercomponents of device 400. Resistor 110 may be located near basebandprocessor 452 or other convenient locations within device 400. Thermalmonitor 135 receives input signals from thermistors 112-114 and resistor110, and generates calibration measurements and temperaturemeasurements. The temperature measurements, after calibration, may beused to manage the power consumption of device 400.

To minimize power consumption, device 400 may include a power managementunit 420 to implement power management functions. In response to thetemperature measurement of thermistors 112-114 and thermal monitor 135,power management unit 420 may adjust the power consumption by thecomponents of device 400, thereby maintaining the temperature of device400 at or just below a critical thermal bound. Power management unit 420reduces the power consumption to reduce heat generation when thetemperature measurement exceeds the critical thermal bound threshold.When the temperature measurement drops below the threshold, powermanagement unit 420 may increase the power supplied to that componentand other components to improve performance. For example, powermanagement unit 420 may adjust the gain settings of power amplifiers456, the voltages supplied by battery 483, the backlight of display 416or other visual output devices 473, the voice/data transmission rateand/or the processing speed of baseline processor 452, as well as otherfunctions of the device components.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

1. An apparatus for thermal management in an electronic device, the apparatus comprising: integrated circuitry that includes an analog-to-digital converter (ADC), and a multiplexer having an output coupled to an input of the ADC; a resistor coupled to a first input of the multiplexer; and a thermistor coupled to a second input of the multiplexer, wherein the resistance of the resistor is about the same as the resistance of the thermistor when the thermistor is below a critical thermal bound of the electronic device.
 2. The apparatus of claim 1, further comprising: a current generator coupled between the ADC and the output of the multiplexer to provide a current to the resistor and the thermistor.
 3. The apparatus of claim 1, wherein the integrated circuitry is located in an integrated circuit package of a baseband processor for wireless communications.
 4. The apparatus of claim 3, wherein the resistor is coupled to a thermistor input pin of the integrated circuit package.
 5. The apparatus of claim 1, wherein the multiplexer receives input signals through a plurality of signal paths, each signal path to include a respective thermistor, where the respective thermistor is associated with one of the following components of the electronic device: a battery, an antenna power amplifier, and a subscriber identity module (SIM) card circuit.
 6. The apparatus of claim 1, wherein the thermistor is placed at or near a component of the electronic device to sense a temperature associated with the component.
 7. An article of manufacture comprising a computer readable medium including instructions that, when executed by a processing system, cause the processing system to: compute a temperature correction, based on an output signal of an analog-to-digital converter (ADC) while an input signal to the ADC is a function of a set current being passed through a resistor; obtain a temperature reading, based on the output of the ADC while the input to the ADC is a function of the set current being passed through a thermistor; and adjust the temperature reading with the temperature correction, to obtain a calibrated temperature that is associated with a component of the electronic device.
 8. The article of manufacture of claim 7, wherein the instructions cause the system to compute the temperature correction by obtaining a first temperature, based on the output signal of the ADC while the input signal to the ADC is a function of the set current through the resistor; and computing a difference between the first temperature and a reference temperature, wherein the resistance of the resistor is about the same as the resistance of the thermistor when the thermistor is at the reference temperature.
 9. The article of manufacture of claim 7, wherein the instructions cause the system to treat the reference temperature as being below a critical thermal bound of the electronic device.
 10. The article of manufacture of claim 9, wherein the critical thermal bound is determined based on a safety limit of a battery and a customer satisfaction limit.
 11. The article of manufacture of claim of claim 8, wherein the resistance of the resistor and the reference temperature fall on a resistance-temperature curve of the thermistor. 